This application relates generally to amplifiers particularly adapted for use in modern computer data bus systems. In such systems, a plurality of signals may be selectively applied to a single data bus through output amplifiers. It is desirable to apply such signals in sinusoidal or nearly sinusoidal form while avoiding spurious signals which contribute to noise. A substantial source of potential noise, and therefore a major problem in noise reduction and elimination of extraneous signals, are the high frequency components introduced into data bus lines by amplifiers not otherwise being driven.
In the art, data bus systems have utilized digital line drivers which, by their design, provide a high impedance when in an "off" state but such drivers cannot be utilized to drive sinusoidal signals, and therefore introduce undesirable frequency components on the data bus. On the other hand, where linear drivers capable of applying sinusoidal signals to a data bus line are utilized, high-current electronic switches must be added intermediate the amplifier output and the data bus to present the desired high output impedance. Such switches require relatively high power to drive, are relatively expensive and large, and further, consume system power since the entire amplifier current passes therethrough when in the "on" state.
By providing a linear amplifier including control means for selectively cutting off the internal operation of the amplifier in response to a low-current control signal, the foregoing disadvantages are avoided.